Takeaways
- Selenium is a trace mineral vital for human health
- It supports thyroid function and immune system strength
- Selenium acts as a powerful antioxidant in the body
- Both deficiency and excess can cause health problems
- Food sources vary based on soil content and geography
- Supplementation may benefit some individuals
What Is Selenium?
Selenium is a trace mineral present in soil, water, and various foods.[1] It’s a necessary nutrient for human health, although the body requires it in only small amounts. Swedish chemist Jöns Jacob Berzelius discovered selenium in 1817.[2]
Initially, scientists believed selenium was harmful to humans.[3] Later studies demonstrated its significance for well-being. In 1957, selenium was recognized as an essential nutrient for animals.[4] By the 1970s, its role in human health became clearer.[5]
Selenium has multiple functions within the body. It aids in the creation of selenoproteins, which are special proteins. These proteins are involved in:
- Making DNA
- Reproducing cells
- Preventing cell damage
- Regulating thyroid hormones
The human body cannot produce selenium; it must be obtained through diet or supplements.[6] The amount found in foods depends on the selenium levels present in the soil where plants are grown or animals graze.[7]
Natural Sources of Selenium
Selenium occurs naturally in a variety of foods. The amount varies based on the geographic location where the food was produced. Selenium levels in soil differ globally, which influences how much is absorbed by plants and animals.
Several factors affect the amount of selenium in soil, such as:
- Rainfall
- Soil pH
- Organic matter content
- Use of selenium-containing fertilizers
Foods that are good sources of selenium include:
- Brazil nuts
- Seafood (tuna, halibut, sardines)
- Organ meats (kidney, liver)
- Poultry
- Eggs
- Mushrooms
- Whole grains
Brazil nuts are exceptionally high in selenium.[8] Consuming just one nut can exceed the daily recommended intake.[9] However, the selenium content within Brazil nuts can vary significantly.
Selenium content in crops differs by region.[10] For instance, wheat from North America typically contains more selenium than wheat from Europe.[11] This is attributed to variations in soil composition.
Selenium levels in animal products also differ. This depends on the animal’s diet. Grass-fed beef frequently contains more selenium than grain-fed beef because the plants they eat reflect the soil’s selenium content.[12]
Selenium in the Body
Absorption and Distribution
The small intestine absorbs selenium from ingested food.[13] The form of selenium affects how well it’s absorbed; organic forms, such as selenomethionine, are absorbed more efficiently than inorganic forms.[14]
Once absorbed, selenium is transported through the blood to different tissues. It is concentrated in the:
- Liver
- Kidneys
- Spleen
- Pancreas
- Testes
Selenium is also present in smaller amounts in other parts of the body. Here’s a breakdown of selenium concentrations in various areas:
Body Part/Fluid | Selenium Content |
---|---|
Liver | Highest |
Kidneys | High |
Muscle | Moderate |
Blood | Low |
Urine | Very Low |
Metabolism
The body processes selenium through several steps. First, it’s converted into forms that cells can use. The primary usable form is selenocysteine, which is then utilized to create selenoproteins.[15]
Selenoproteins perform many functions in the body. They:
- Act as antioxidants
- Help make thyroid hormones
- Support immune function
- Aid in reproduction
Glutathione peroxidase is an important selenoprotein.[16] This enzyme protects cells from damage by neutralizing harmful molecules called free radicals.
Selenium’s role as an antioxidant is complex.[17] It supports the formation and activation of antioxidant enzymes. These enzymes circulate throughout the body, protecting cells in different tissues from oxidative stress.
Health Benefits of Selenium
Thyroid Function
Selenium is critical for thyroid health.[18] The thyroid gland contains more selenium per gram than any other organ.[19] Selenium helps produce and regulate thyroid hormones.[20]
Thyroid hormones control many bodily functions including:
- Metabolism
- Growth
- Development
- Body temperature
Insufficient selenium can hinder thyroid function. This may result in conditions such as:
- Hypothyroidism
- Hashimoto’s disease
- Graves’ disease
Some studies suggest that selenium supplements may benefit individuals with thyroid problems.[21] However, further research is needed to confirm these findings.
Immune System Support
Selenium strengthens the immune system.[22] It aids the body in producing and utilizing white blood cells, which defend against harmful bacteria and viruses.
Research indicates that selenium may lower the risk of certain infections. For example, individuals with higher selenium levels may be less likely to contract:
- Influenza
- HIV
- Hepatitis C
Selenium also contributes to the production of antibodies.[23] These proteins assist in identifying and neutralizing threats to our health.
Antioxidant Properties
Selenium is a potent antioxidant.[24] It protects cells from the damage caused by free radicals, which are unstable molecules that can harm DNA and cells.
Here’s how selenium functions as an antioxidant:
- It becomes part of antioxidant enzymes
- These enzymes spread throughout the body
- The enzymes neutralize free radicals
- This prevents damage to cells and DNA
- Over time, this may reduce the risk of chronic diseases
By counteracting oxidative stress, selenium may help prevent:
- Heart disease
- Some types of cancer
- Cognitive decline
Cognitive Health
Selenium might have a positive impact on brain function. Some studies connect higher selenium levels with improved cognitive performance.[25]
As we age, our brains become more susceptible to oxidative stress. Selenium’s antioxidant properties may help protect brain cells, potentially slowing cognitive decline.[26]
Research in this area is still underway. Initial studies show promise, but more evidence is required. Scientists are investigating selenium’s role in:
- Memory
- Mood
- Alzheimer’s disease prevention
Cardiovascular Health
Selenium may promote heart health. Its antioxidant effects could protect against heart disease. Some studies suggest selenium might:
- Reduce inflammation
- Lower bad cholesterol levels
- Prevent blood clots
However, the evidence is inconsistent.[27] Some research finds no clear relationship between selenium and heart health. More studies are needed to fully understand this connection.
Selenium Deficiency
Causes
Selenium deficiency is uncommon in most countries. However, it can occur in regions with soil that has low selenium content. Other factors that may lead to a deficiency include:
- Poor diet
- Digestive disorders that impair absorption
- Kidney dialysis
- HIV infection
Individuals at higher risk of selenium deficiency include:
- Those living in low-selenium regions
- People with severe digestive issues
- Individuals on long-term intravenous feeding
Symptoms
Selenium deficiency often does not cause obvious symptoms. However, when symptoms do appear, they can include:
- Weakness
- Fatigue
- Hair loss
- Weakened immune system
- Fertility problems
- Mood changes
In severe cases, selenium deficiency can lead to more serious health issues.[28] These may impact the heart, bones, and the immune system.
Health Consequences
Long-term selenium deficiency can have significant consequences. It may increase the risk of:
- Keshan disease (a type of heart problem)
- Kashin-Beck disease (a bone disorder)
- Thyroid dysfunction
- Weakened immune system
- Cognitive decline
- Cardiovascular disease
In areas with very low selenium intake, programs that include supplementation have been beneficial.[29] They have lowered the occurrence of Keshan disease and other health problems.
Selenium Toxicity
Causes
While selenium deficiency is uncommon, toxicity can occur as well. This typically happens from consuming too many supplements. It’s very rare to get too much selenium from food alone.[30]
Risk factors for selenium toxicity include:
- Over-supplementation
- Accidental ingestion of selenium-containing products
- Living in areas with very high soil selenium levels
Symptoms
Signs of selenium overload can include:
- Garlic breath odor
- Nausea
- Diarrhea
- Skin rashes
- Brittle nails
- Hair loss
Severe cases might result in more serious symptoms:
- Nerve damage
- Fatigue
- Irritability
- Tremors
- Kidney failure
Health Consequences
Long-term high selenium intake may result in extended health issues. These could include:
- Type 2 diabetes
- Skin lesions
- Nervous system problems
- Cardiovascular issues
Some studies have associated high selenium levels with a higher risk of prostate cancer.[31] However, additional research is needed to confirm this association.
Recommended Intake
The amount of selenium needed varies based on age and life stage. Here are the Recommended Dietary Allowances (RDAs) for selenium:
Age | Male (mcg/day) | Female (mcg/day) |
---|---|---|
0-6 months | 15 | 15 |
7-12 months | 20 | 20 |
1-3 years | 20 | 20 |
4-8 years | 30 | 30 |
9-13 years | 40 | 40 |
14+ years | 55 | 55 |
Pregnancy | – | 60 |
Breastfeeding | – | 70 |
These amounts are the average daily intake needed to meet the needs of most healthy individuals. Certain factors that could affect selenium needs include:
- Overall health status
- Medications
- Digestive issues
- Alcohol consumption
- Smoking
It’s important to understand that more is not always better. The upper limit for adults is 400 mcg per day.[32] Intakes above this level could cause harm.
Selenium Supplements
Types
Selenium supplements are available in different forms. Common types include:
- Selenomethionine
- Sodium selenite
- Selenium-enriched yeast
Each form has varying absorption rates and effects within the body. Selenomethionine is often considered the most easily absorbed form.[33]
Usage
Guidelines for taking selenium supplements include:
- Follow the dosage instructions on the label
- Don’t exceed the recommended daily allowance
- Take with food to improve absorption
- Spread doses throughout the day if taking higher amounts
It’s essential to consult a healthcare provider prior to starting any supplement. They can help determine if you need supplemental selenium and what the appropriate dosage is for you.
Safety
While selenium supplements can be helpful, they also come with some risks. Precautions to consider include:
- Don’t exceed the upper limit of 400 mcg per day
- Be aware of selenium content in multivitamins
- Watch for signs of toxicity
- Inform your doctor of all supplements you’re taking
Selenium can interact with certain medications, including:
- Some chemotherapy drugs
- Statins (cholesterol-lowering medications)
- Niacin
- Antacids
Always consult with a healthcare provider before combining selenium with any medications.
Selenium in Special Populations
Pregnancy and Breastfeeding
Selenium requirements increase during pregnancy and breastfeeding to support fetal growth and development.[34] The RDA for pregnant women is 60 mcg daily, while for breastfeeding women, it’s 70 mcg daily.[35]
Adequate selenium during pregnancy may help:
- Reduce the risk of preeclampsia
- Support fetal brain development
- Strengthen the baby’s immune system
However, excessive selenium can be harmful. Pregnant women should avoid high-dose supplements unless prescribed by a doctor.[36]
Elderly
As people age, their bodies may not absorb nutrients as efficiently. This includes selenium.[37] Older adults might need to be particularly mindful of their selenium intake.
Some studies suggest that higher selenium levels in older adults are associated with:
- Better cognitive function
- Reduced risk of depression
- Improved immune response
However, additional research is needed to confirm these advantages. Older adults should target the RDA of 55 mcg per day, unless otherwise advised by a doctor.[38]
Athletes
Athletes may have increased selenium requirements because intense exercise can increase oxidative stress in the body.[39] Selenium’s antioxidant properties might help counteract this.
Potential advantages of sufficient selenium for athletes may include:
- Reduced muscle damage
- Improved recovery
- Enhanced immune function
However, there isn’t evidence that extra selenium boosts performance.[40] Athletes should prioritize obtaining enough selenium through a balanced diet. Supplements are seldom necessary unless advised by a sports nutritionist.
Selenium and Disease Prevention
Cancer
The relationship between selenium and cancer is intricate.[41] Some studies suggest selenium might help prevent certain cancers, while others show no benefit or possible harm at higher doses.
Possible anti-cancer effects of selenium include:
- Reducing DNA damage
- Slowing tumor growth
- Enhancing immune function
However, results vary depending on the cancer type and individual factors. A large study called SELECT found that selenium supplements did not reduce prostate cancer risk.[42] In some situations, high selenium levels might even increase risk.[43]
Further research is necessary to clarify selenium’s role in cancer prevention. Currently, it’s best to get selenium from food sources instead of supplements.[44]
HIV/AIDS
Selenium may play a role in HIV/AIDS management. People with HIV often have low selenium levels. This could be due to poor nutrition or the impact of the virus itself.
Studies have determined that selenium status can influence:
- Disease progression
- Immune function
- Quality of life in HIV patients
Some research indicates that selenium supplements might slow down HIV progression.[45] However, more studies are needed to verify these effects.
Individuals with HIV should discuss selenium intake with their healthcare team. Proper nutrition, including sufficient selenium, can support overall health and immune function.
Diabetes
The connection between selenium and diabetes is not yet clear.[46] Some studies indicate that high selenium levels might increase the risk of diabetes. Others show no link, or even suggest a protective effect.
Possible effects of selenium on diabetes may include:
- Influencing insulin sensitivity
- Affecting blood sugar regulation
- Impacting oxidative stress in diabetic patients
A review of studies discovered that both very low and very high selenium levels might raise the risk of diabetes.[47] The safest approach is to strive for the recommended daily intake through food sources.
People with diabetes should discuss selenium intake with their doctor. They can help determine if supplements are necessary or potentially harmful.
Testing for Selenium Status
Measuring selenium levels in the body can be beneficial in certain situations. Common tests include:
- Blood tests (serum or plasma selenium)
- Hair analysis
- Nail clippings analysis
- Urine tests
Each testing method has advantages and disadvantages. Blood tests are most common but may not reflect long-term status.[48] Hair and nail tests can show selenium levels over time, but are less accurate.[49]
Interpreting selenium test results requires expert knowledge. Factors to consider include:
- Age
- Sex
- Diet
- Health conditions
- Medications
Normal selenium ranges can vary based on these factors. A healthcare provider can assist in making sense of test results. They will take your overall health and any symptoms into account when interpreting the numbers.
Selenium in the Food Industry
The food industry uses selenium in different ways. One typical practice is food fortification, which involves adding selenium to foods to improve their nutritional content.[50]
Some products that may be fortified with selenium include:
- Bread
- Cereals
- Pasta
- Dairy products
Another method involves producing selenium-enriched foods. Farmers can do this by adding selenium to the soil or animal feed, which results in higher selenium content in crops and animal products.[51]
Here’s a comparison of selenium levels in regular versus enriched foods:
Food Item | Regular (mcg/100g) | Enriched (mcg/100g) |
---|---|---|
Wheat bread | 10-30 | 60-80 |
Eggs | 20-30 | 30-50 |
Milk | 1-3 | 5-10 |
Mushrooms | 5-10 | 30-70 |
Enriched foods can help prevent deficiencies in areas with low selenium levels. However, it’s important to monitor intake to avoid overconsumption.
Environmental Impact of Selenium
Selenium is a component in ecosystems worldwide. It’s vital for many plants and animals. However, excessive selenium can harm the environment.
In nature, selenium cycles through:
- Soil
- Water
- Air
- Living organisms
Human actions can disrupt this cycle. Sources of selenium pollution include:
- Coal combustion
- Mining operations
- Agricultural runoff
- Industrial processes
High levels of selenium in water can harm aquatic life. It can build up in fish, leading to deformities or reproductive issues.[52]
Efforts to manage selenium in the environment include:
- Monitoring water and soil levels
- Treating contaminated areas
- Regulating industrial emissions
- Developing selenium-tolerant crops
Balancing human needs with environmental protection is an ongoing challenge. Researchers are working to find sustainable ways to manage selenium resources.
Future Research and Developments
Scientists are continually studying selenium’s effects on health. Current research topics include:
- Selenium’s role in cancer prevention and treatment
- Its impact on cognitive function and brain health
- Potential benefits for heart disease and diabetes
- Optimal intake levels for different populations
- New ways to measure selenium status in the body
Challenges in selenium research include:
- Variability in soil selenium levels worldwide
- Differences in how individuals metabolize selenium
- Interactions with other nutrients and medications
- Long-termeffects of selenium supplementation
Potential new applications of selenium in medicine and nutrition are developing. These include:
- Targeted selenium therapies for specific health conditions
- Development of new selenium-enriched foods
- Use of selenium nanoparticles in medical treatments
- Personalized selenium recommendations based on genetic factors
As research advances, our understanding of selenium’s role in health will increase.[53] This could result in more effective methods to utilize this mineral for disease prevention and treatment.
FAQ: People Also Ask
In summary, selenium is a vital mineral with wide-ranging impacts on human health. It plays diverse and important roles, from supporting thyroid function to boosting the immune system. Although most people can obtain sufficient selenium through a balanced diet, some populations may benefit from paying closer attention to their selenium intake. It’s crucial to understand the balance between adequate intake and the risks of deficiency or toxicity. As with many nutrients, moderation is key. Too little selenium can cause health problems, while too much can also be harmful. The varying levels of selenium in foods, affected by geographic and agricultural factors, complicate managing selenium intake. This emphasizes the importance of eating a variety of foods and being aware of local sources. Ongoing research continues to reveal new aspects of selenium’s functions in the body. Future studies may lead to more specific uses of selenium in medicine and nutrition, and may also help refine guidelines for optimal intake across different populations and health conditions. Individuals with concerns about their selenium status should seek advice from a healthcare provider or registered dietitian.[54] They can provide individualized recommendations based on factors such as diet, health status, and geographic location. As our knowledge of selenium expands, so does our capacity to maximize its benefits while reducing risks. This essential mineral, once considered toxic, has proven to be a valuable component of human health. Continued research and public awareness will be key to maximizing the potential of selenium in nutrition and medicine.What foods are high in selenium?
Can you take too much selenium?
What does selenium do for your body?
How much selenium do I need daily?
Is selenium good for hair growth?
Can selenium help with weight loss?
Does selenium interact with any medications?
Is selenium good for skin health?
Selenium is naturally occurring and found in soil, water, and is absorbed by plants and animals that are part of the food chain.
Source: “Enhancing the Activity of Carboxymethyl Cellulase Enzyme Using Highly Stable Selenium Nanoparticles Biosynthesized by Bacillus paralicheniformis Y4” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9324468/
Berzelius discovered selenium in 1817 while investigating a sulfur byproduct from a sulfuric acid factory.
Early observations of selenium showed toxic effects, which led to initial beliefs that it was harmful. It was later discovered that small amounts were necessary for health.
The 1957 recognition of selenium as essential for animals was pivotal in understanding its role in biological systems. Subsequent research further revealed its importance for humans.
Source: “The Effects of Selenium on Bone Health: From Element to Therapeutics” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8780783/
In the 1970s, there was considerable work that began to indicate its importance in human health.
The human body cannot synthesize selenium, making dietary intake the only way to obtain this nutrient.
The amount of selenium present in food is heavily influenced by the selenium concentration in the soil where the food source is grown or raised.
Brazil nuts are known for their high selenium concentration, making them a good source of this nutrient. However, it’s important to note that selenium levels can vary due to differences in soil content.
Due to the high selenium content, just one or a few brazil nuts can provide more than the daily recommended selenium intake, so overconsumption could be harmful.
The geographic location of crop cultivation influences selenium content due to the soil’s variability in selenium.
Soil composition and other environmental factors result in regional variations in selenium content in crops such as wheat.
Selenium levels in animal products are directly influenced by the selenium content in their feed. Grass-fed cattle consume plants that have absorbed selenium from the soil.
The small intestine is the main site of selenium absorption into the body.
Source: “Improvement of selenium enrichment in Rhodotorula glutinis X-20 through combining process optimization and selenium transport” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6682361/
Organic forms of selenium such as selenomethionine are generally absorbed more effectively compared to inorganic forms, leading to better utilization by the body.
Selenocysteine is the key amino acid form that is incorporated into selenoproteins, which are proteins containing selenium, and crucial for various biological functions.
Glutathione peroxidase is a crucial selenoprotein, and it helps protect cells from oxidative damage.
Selenium’s antioxidant functions are intricate and involves its role in the production and activity of antioxidant enzymes.
Selenium is necessary for the synthesis and metabolism of thyroid hormones. Adequate selenium is needed for optimal thyroid health.
The thyroid gland has a unique need for selenium compared to other organs. This underscores its importance for thyroid hormone metabolism.
Selenium is crucial for the enzymes involved in thyroid hormone production and conversion.
Some studies suggest that selenium supplements may benefit certain individuals with thyroid conditions, but the effectiveness and specific use cases are still under investigation.
Selenium plays a vital role in immune cell production and function. It also helps support the immune response by acting as an antioxidant.
Source: “The Immunomodulatory Effects of Selenium: A Journey from the Environment to the Human Immune System” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11479232/
Selenium plays an important role in antibody production, which is crucial for immune defense.
Selenium functions as an antioxidant by supporting the activity of antioxidant enzymes that protect cells from free radicals.
Some research suggests that adequate selenium levels may correlate with better cognitive function, but more research is needed to fully understand the relationship.
Selenium’s antioxidant properties could help to reduce damage from free radicals. This may help to reduce risk of cognitive decline, but more studies are needed.
Studies have yielded inconsistent results with some studies indicating potential benefits while others showing no clear relationship between selenium and heart health.
Severe selenium deficiency can lead to a range of health problems affecting the heart, bones, and the immune system.
Programs involving selenium supplementation have demonstrated health benefits in regions with low selenium levels in the population.
Selenium toxicity is rare from dietary sources alone, but is more likely to result from consuming excessive selenium supplements.
Some studies have suggested a possible link between high selenium intake and an elevated risk of prostate cancer, but research is inconclusive.
Exceeding the upper limit of 400 mcg per day for selenium intake can be dangerous and could cause toxicity.
Among various forms of selenium, selenomethionine is thought to be more readily absorbed by the body.
Pregnancy and breastfeeding require additional selenium to support both maternal health and the baby’s growth and development.
The Recommended Dietary Allowance (RDA) for selenium is slightly higher for pregnant and breastfeeding women than the general adult population.
Pregnant women should be careful to consume adequate selenium, but should be careful about taking high doses unless prescribed by their doctor.
The body’s ability to absorb nutrients, including selenium, may decline as people age, which emphasizes the need to monitor intake in older adults.
Unless a healthcare provider recommends otherwise, older adults should aim to consume at least the recommended dietary allowance (RDA) of 55 mcg daily.
Intense exercise can lead to increased oxidative stress in the body, potentially increasing selenium requirements. More research is needed on the topic.
While selenium is important for health, extra selenium beyond what’s needed to avoid a deficiency does not offer enhanced athletic performance.
The role of selenium in cancer is complex, with some studies showing potential benefits and others showing possible risks, particularly at higher doses.
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) showed that selenium supplementation did not reduce the risk of prostate cancer.
Source: “Selenium for preventing cancer” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6491296/
Studies have shown that in certain scenarios, high selenium intake may lead to a higher risk of some cancers, but this is not always the case and more research is needed.
Getting selenium from a balanced diet is generally recommended. Supplementation should be done under guidance of a healthcare professional.
Some preliminary studies suggest that selenium supplements might have a positive effect on HIV progression, but larger, more conclusive studies are required.
Studies on the connection between selenium and diabetes have produced varying results, making the connection unclear.
A review of studies indicated a U-shaped relationship between selenium and the risk of diabetes, with both very low and very high levels potentially increasing risk.
Source: “Selenium and Selenoproteins in Health” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10216560/
Blood tests for selenium are a common method, but only provide a snapshot in time, and may not be reflective of long-term status.
Hair and nail tests for selenium can provide a longer-term view of selenium status but are not as accurate as blood tests.
The food industry uses selenium fortification to enhance the nutritional value of various food products.
Farmers can enrich foods by supplementing the soil or animal feed with selenium, thus increasing its level in crops and animal products.
High concentrations of selenium in water can lead to bioaccumulation, causing harm to aquatic animals like fish, leading to deformities and reproductive problems.
Ongoing research is leading to deeper knowledge about selenium’s functions in the body, potential benefits, and potential risks.
Individuals with questions or concerns about selenium should seek guidance from a medical professional.
The list represents the most common food sources that are high in selenium. The exact amount will vary.
Selenium toxicity is possible if high doses are consumed through supplementation, or, very rarely, dietary sources. The upper limit is 400 mcg per day.
Selenium supports thyroid function, and acts as an antioxidant, and it is essential to the immune system. Further research is being done to show what other roles it may have.
55 mcg is the Recommended Daily Allowance (RDA) of selenium for most adults. This can usually be met by eating a balanced diet without any need for supplementation.
Selenium deficiency can cause hair loss, but there’s no indication that supplementation will cause hair growth in people who are not deficient.
While adequate selenium intake is important for the overall function of the body, there is no evidence that it directly causes weight loss.
Selenium may interact with some chemotherapy drugs, statins, niacin, and sedatives. This is why it’s very important to inform a doctor about all supplements you are taking.
Selenium’s antioxidant properties might help protect the skin from sun damage, and generally support skin health, although more research is needed.